1. Field of the Invention
The present invention relates generally to an illumination apparatus including a wavelength conversion unit.
2. Description of the Related Art
FIG. 11 shows a light-emitting apparatus, which is a conventional example of an illumination apparatus including a wavelength conversion unit. The light-emitting apparatus has an excitation light source 10 that emits excitation light 1, a wavelength conversion member 30 that absorbs the excitation light 1 emitted from the excitation light source 10 and performs wavelength conversion to emit illumination light 2 in a predetermined wavelength band, and an optical fiber 20 that leads the excitation light 1 emitted from the excitation light source 10 to the wavelength conversion member 30. The excitation light source 10 includes a light-emitting element 11 and leads light emitted from the light-emitting element 11 to the optical fiber 20 from an exit portion 12. In order to efficiently lead the light emitted from the light-emitting element 11 to the exit portion 12, a lens 13 is provided between the light-emitting element 11 and the exit portion 12. One end of the optical fiber 20 is connected to the exit portion 12, and the other end is provided with an output portion 21 from which the light is led to the outside. The output portion 21 includes a wavelength conversion member 30 to constitute a wavelength conversion unit. A fluorescent material 31 is used as the wavelength conversion member 30. The wavelength conversion member 30 absorbs the excitation light 1 emitted from the excitation light source 10 and performs the wavelength conversion to emit the illumination light in the predetermined wavelength band.
In a conventional illumination apparatus, when the wavelength conversion member is irradiated with the excitation light, the wavelength conversion member emits light in which wavelength-converted light obtained by converting the excitation light by the wavelength conversion member is mixed with the excitation light transmitted through the wavelength conversion member without being converted into the wavelength-converted light. An intensity of the excitation light that exits from the optical fiber and then enters the wavelength conversion member has a distribution in which the intensity is maximum at the center (a region near a central axis of the optical fiber) and decreases as getting closer to the periphery from the center. Since the excitation light is subjected to the wavelength conversion at a point where it is absorbed, so that the wavelength-converted light is emitted in all directions, and a part of the wavelength-converted light is repeatedly scattered in the wavelength conversion member and then exits, it exits with being uniformed to some extent. On the other hand, since the excitation light transmitted without being converted into the wavelength-converted light has high direct advance properties, the transmitted excitation light exits with high intensity at the center. As a result, an intensity ratio of the excitation light and the wavelength-converted light differs depending on the center and a region apart from the center, and color shading occurs in the light having the transmitted excitation light and the wavelength-converted light mixed therein.